Performance comparison between servo motor and stepper motor - News - Global IC Trade Starts Here Free Join
Stepper motors are widely used in modern digital control systems as an open-loop control mechanism. However, with the rise of all-digital AC servo systems, AC servo motors have become more prevalent in such applications. This shift is driven by the need for higher precision, better performance, and more reliable operation. While both types of motors share some similarities in control methods—such as using pulse and direction signals—they differ significantly in terms of accuracy, speed, torque, and overall reliability.
First, the control precision varies greatly between the two. Stepper motors typically have step angles of 1.8°, 0.9°, or even smaller when using subdivision techniques. Some high-performance models, like those from SANYO DENKI, can be configured to step sizes as small as 0.036°. In contrast, AC servo motors rely on encoders at the motor shaft to ensure accuracy. For example, a standard 2000-line encoder provides a pulse equivalent of 0.045°, while a 17-bit encoder offers a much finer resolution of 0.0027466°, which is about 1/655th of a 1.8° step. This makes AC servos far more precise for high-accuracy applications.
Second, low-speed performance differs significantly. Stepper motors tend to vibrate at low speeds due to their inherent working principle, which can cause instability and reduce system efficiency. To mitigate this, damping or subdivision techniques are often required. On the other hand, AC servo motors operate smoothly even at low speeds, thanks to built-in resonance suppression and frequency analysis functions that help identify and eliminate potential vibration points.
Third, torque characteristics vary. Stepper motors experience a drop in torque as speed increases, limiting their maximum operating speed to around 300–600 RPM. AC servo motors, however, maintain constant torque up to their rated speed (often 2000–3000 RPM), and then transition to constant power mode beyond that. This makes them more suitable for high-speed and high-torque applications.
Fourth, overload capacity is another key difference. AC servo motors can handle significant short-term overloads, with some models offering up to three times their rated torque. This helps overcome inertia during startup without requiring oversized motors. Stepper motors, on the other hand, lack this capability, leading to potential inefficiencies and wasted torque in normal operation.
Fifth, operational performance is crucial. Stepper motors are open-loop systems, meaning they can lose steps if the speed is too high or the load is too heavy. AC servo systems, being closed-loop, provide feedback through the encoder, ensuring more accurate and stable control. This results in fewer errors and more reliable performance under varying conditions.
Sixth, speed response time is a major advantage of AC servo systems. While a stepper motor may take 200–400 milliseconds to accelerate from rest to its operating speed, an AC servo motor like the Shanyang 400W model can reach 3000 RPM in just a few milliseconds. This makes them ideal for applications requiring fast start and stop cycles.
In conclusion, while AC servo motors outperform stepper motors in most aspects, including precision, speed, torque, and reliability, stepper motors are still commonly used in cost-sensitive or less demanding applications. When designing a control system, it's important to evaluate factors like performance requirements, budget, and application complexity to choose the best motor type for the task.
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